This invention relates to color cathode ray tubes or other color video displays having front surface anti-glare treatments.
It is known to use an interference type anti-reflective coating on the face of a cathode ray tube in applications where the cost of such coatings can be tolerated and where finger contact is not contemplated.
It is also known to randomly roughen or perturb the front surface of a cathode ray tube, or to overlay a transparent membrane or panel, such that it scatters reflected light. This random roughening has been accomplished by vapor or submerged etching, mold roughening, surface grinding, sprays and in various other ways.
However, roughening the front surface of a CRT or an overlay thereon, degrades the underlying cathodeluminescing image by dispersing the image light emitted from the phosphor screen. The roughened surface approach is practical, however, in many applications because the angular dispersion of emitted image light is substantially less than the angular scattering of reflected light.
The surface roughening approach is a satisfactory solution to the front surface glare problem for most applications of monochrome and color cathode ray tubes, however, attempts to apply the same surface roughening techniques to certain shadow mask color cathode ray tubes has been found to produce a conspicuous visual phenomenon which has been described as a "sparkle". The sparkle phenomenon appears to be less conspicuous in line screen color CRTs than in dot screen type CRTs (those with shadow masks having circular holes). One application in which the sparkle phenomenon can be disturbing is a high resolution shadow mask color CRT of the flat tension mask type overlaid with a plastic membrane, such as is used in certain touch-responsive systems. The membrane is of a type having a particulate anti-scratch/anti-glare surface coating.
This sparkle is believed to result from random moire' effects. The visual impression of this random moire' or sparkle is one of little pinpoints of light or sparkles (and occasionally dark spots) which come and go. They appear to move as the observer's head is moved, sometimes in the same direction as the head movement and sometimes in the opposite direction.